Ion to neutral control for wafer processing with dual plasma source reactor

ABSTRACT

The disclosed techniques relate to methods and apparatus for etching a substrate. A plate assembly divides a reaction chamber into a lower and upper sub-chamber. The plate assembly includes an upper and lower plate having apertures therethrough. When the apertures in the upper and lower plates are aligned, ions and neutral species may travel through the plate assembly into the lower sub-chamber. When the apertures are not aligned, ions are prevented from passing through the assembly while neutral species are much less affected. Thus, the ratio of ion flux:neutral flux may be tuned by controlling the amount of area over which the apertures are aligned. In certain embodiments, one plate of the plate assembly is implemented as a series of concentric, independently movable injection control rings. Further, in some embodiments, the upper sub-chamber is implemented as a series of concentric plasma zones separated by walls of insulating material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 14/033,241, filed Sep. 20, 2013, titled “ION TONEUTRAL CONTROL FOR WAFER PROCESSING WITH DUAL PLASMA SOURCE REACTOR,”which is a continuation-in-part of U.S. application Ser. No. 12/850,552(now issued as U.S. Pat. No. 8,869,742), titled “PLASMA PROCESSINGCHAMBER WITH DUAL AXIAL GAS INJECTION AND EXHAUST,” filed Aug. 4, 2010,each of which is incorporated herein by this reference for all purposes.

BACKGROUND

One operation frequently employed in the production of semiconductors isan etching operation. In an etching operation, one or more materials arepartly or wholly removed from a partially fabricated integrated circuit.Plasma etching is often used, especially where the geometries involvedare small, high aspect ratios are used, or precise pattern transfer isneeded. Typically, a plasma contains electrons, ions and radicals. Theradicals and ions interact with a substrate to etch features, surfacesand materials on the substrate.

As device dimension shrink, plasma etching processes need to beincreasingly precise and uniform in order to produce quality products.One driving factor for decreasing device dimensions is the push toprovide more devices per substrate. A related factor is the move fromplanar to 3D transistor structures (e.g., FinFET gate structures forlogic devices) and advanced memory structures (e.g., MagnetoresistiveRandom Access Memory (MRAM) and Resistive Random Access Memory (ReRAM)).In order to achieve such precise and uniform processes, differentprocesses must be optimized based on several relevant factors (e.g., theapplication for which the device will be used, the chemistry involved,the sensitivity of the substrate, etc.). Among other factors, a fewimportant variables that may be optimized in an etching process includethe flux of ions to a substrate, the flux of radicals to a substrate,and the related ratio between these two fluxes.

Because different processes are optimized in different ways, anapparatus which is suitable for a first etching process may not besuitable for a second etching process. Due in part to limited space inprocessing facilities, as well as the cost of semiconductor fabricationequipment, it is desirable for a semiconductor fabrication apparatus tobe able to provide a wide range of processing conditions over asubstrate. Further, it may be desirable for a semiconductor apparatus tobe able to provide a wide range of processing conditions over differentparts of a substrate during processing to combat certain geometricnon-uniformities. This consideration is especially important where largesubstrates (e.g., 300 mm and especially 450 mm diameter) are beingprocessed, as the geometric non-uniformities are exacerbated in suchlarge work pieces. In this way, a single apparatus may be used for manydifferent applications to achieve uniform results. The techniquesdescribed herein are especially useful for performing multi-step etchprocesses such as those associated with FinFET structures andback-end-of-line (BEOL) processing such as certain dual Damasceneprocesses, particularly when performed on large substrates. Thedisclosed embodiments may be particularly useful in certain advancedtechnology nodes such as the 40 nm node, the 10 nm node, and the 7 nmnode.

SUMMARY

Certain embodiments herein relate to apparatus and methods for etchingsubstrates. In one aspect of the embodiments herein, an apparatus foretching substrates includes (a) a reaction chamber, (b) a plate assemblypositioned in the reaction chamber thereby dividing the reaction chamberinto an upper sub-chamber and a lower sub-chamber, where the plateassembly includes: (i) a first plate, and (ii) a second plate includingat least two substantially concentric plate sections that areindependently rotatable with respect to the first plate, where the firstplate and second plate have apertures extending through the thickness ofeach plate, (c) one or more gas inlets to the upper sub-chamber, (d) oneor more gas outlets to the reaction chamber designed or configured toremove gas from the reaction chamber, and (e) a plasma generation sourcedesigned or configured to produce a plasma in the upper sub-chamber.

In some embodiments, the apparatus includes at least three substantiallyconcentric plate sections. In these or other cases, at least some of theapertures in at least one of the plates of the plate assembly may havean aspect ratio between about 0.2-0.4. At least one of the plates of theplate assembly may have an open area between about 40-60%. In certainimplementations, the plate sections of the second plate include aninsulating material, and the first plate includes a conductive material.The upper sub-chamber may be divided into a plurality of concentricplasma zones separated by one or more insulating walls. In variousembodiments, a controller may be used to implement an etching method.For example, the controller may be designed or configured to rotate oneor more of the concentric plate sections to control center to edge etchconditions on the substrate. The controller may also be designed orconfigured to move at least a first concentric plate section relative tothe first plate to orient the apertures of the first and second platesto control an ion to radical flux ratio.

In another aspect of the embodiments herein, an apparatus for etchingsubstrates is provided, including (a) a reaction chamber having an uppersub-chamber and a lower sub-chamber, where the upper sub-chamberincludes at least two substantially concentric plasma zones, where eachplasma zone is isolated from other plasma zones by one or moreinsulating walls, (b) a plate assembly positioned between the uppersub-chamber and lower sub-chamber and including a first plate and asecond plate, where each plate has apertures extending through thethickness of the plate, and where the second plate is rotatable withrespect to the first plate, (c) one or more gas inlets to the uppersub-chamber, (d) one or more gas outlets to the lower sub-chamberdesigned or configured to remove gas from the lower sub-chamber, and (e)a plasma generation source designed or configured to produce a plasma inthe upper sub-chamber.

The apparatus may also include a translation causing mechanism designedor configured to move at least one plate of the plate assembly towardsand away from the other plate of the plate assembly, such that adistance between the first and second plate is variable. In some cases,at least one of the plates may be designed or configured to act as ashowerhead for delivering gases to the upper or lower sub-chambers.There is typically some distance between the first and second plates. Insome embodiments this distance is between about 1-6 mm. At least oneplate of the plate assembly may be between about 3-20 mm thick. Varioustypes of plasma generation sources may be used. In one example, theplasma generation source is designed or configured to produce aninductively coupled plasma. The number of concentric plasma zones mayalso vary. In some embodiments, the upper sub-chamber includes at leastthree substantially concentric plasma zones. Various implementationsutilize a controller configured to perform an etching method. In oneexample, the controller is designed or configured to independentlycontrol plasma generation in the concentric plasma zones and therebycontrol center to edge conditions on the substrate. The controller mayalso be designed or configured to move at least one concentric platesection relative to the first plate to orient the apertures of the firstand second plates to control an ion to radical flux ratio.

In a further aspect of the disclosed embodiments, a method of etching asubstrate is provided, including (a) receiving a substrate in a reactionchamber of an etching apparatus including: (i) a plate assemblypositioned in the reaction chamber and thereby dividing the reactionchamber into an upper sub-chamber and a lower sub-chamber, where theplate assembly includes a first plate and a second plate, where thesecond plate includes at least two concentric sections, where theconcentric sections are independently rotatable with respect to thefirst plate, and where the first plate and second plate have aperturesextending through the thickness of each plate, (ii) one or more gasinlets to the upper sub-chamber, (iii) one or more gas outlets to thelower sub-chamber designed or configured to remove gas from the lowersub-chamber, and (iv) a plasma generation source designed or configuredto produce a plasma in the upper sub-chamber, (b) flowing a plasmagenerating gas into the upper sub-chamber and generating a plasma, (c)flowing neutral species present in the plasma from the uppersub-chamber, through the plate assembly, and into the lower sub-chamber,and (d) etching the substrate.

The method may also include aligning at least some apertures in theupper and lower plates of the plate assembly such that ions flow fromthe upper sub-chamber, through the plate assembly, and into the lowersub-chamber. In some cases, different flux ratios of radicals to ionsare achieved through different portions of the plate assembly. Forexample, a first flux ratio of radicals to ions through a first portionof the plate assembly may be different from a second flux ratio ofradicals to ions through a second portion of the plate assembly. In someembodiments, the method also includes controlling a flux ratio ofradicals to ions through the plate assembly by rotating at least one ofthe concentric sections of the second plate. The method may also includeapplying a bias to a substrate support positioned in the lowersub-chamber. The bias applied to the substrate support may produce aplasma in the lower sub-chamber. In other cases, however, the biasapplied to the substrate support does not produce a plasma in the lowersub-chamber. In certain cases, the method may include applying a bias toone or more plates of the plate assembly. In a particular embodiment,different levels of bias are applied to the different concentric platesections of the second plate. The method may also include rotating oneor more of the concentric plate sections to control center to edge etchconditions on the substrate.

In another aspect of the disclosed embodiments, a method of etching asubstrate is provided, including (a) receiving a substrate in a reactionchamber of an etching apparatus having: (i) an upper sub-chamber and alower sub-chamber, where the upper sub-chamber includes at least twosubstantially concentric plasma zones, where each plasma zone isisolated from other plasma zones by one or more insulating walls, (ii) aplate assembly positioned between the upper sub-chamber and lowersub-chamber and including a first plate and a second plate, where eachplate has apertures extending through the thickness of the plate, andwhere the second plate is rotatable with respect to the first plate,(iii) one or more gas inlets to the upper sub-chamber, (iv) one or moregas outlets to the lower sub-chamber designed or configured to removegas from the lower sub-chamber, and (v) a plasma generation sourcedesigned or configured to produce a plasma in the upper sub-chamber, (b)flowing plasma generating gas into and generating a plasma in eachplasma zone, (c) flowing neutral species present in the plasmas from theplasma zones, through the plate assembly, and into the lowersub-chamber, and (d) etching the substrate.

The method may also include flowing plasma generating gas of a firstcomposition into a first plasma zone and flowing plasma generating gasof a second composition into a second plasma zone to accomplishoperation (b). The first composition and second composition may bedifferent (e.g., they may include different gases, or differentconcentrations of the same gases). In these or other cases, operation(b) may include generating a first plasma in a first plasma zone and asecond plasma in a second plasma zone, where the first plasma and secondplasma have different densities. The method may also include controllingan ion to neutral flux ratio through the plate assembly by changing adistance between the first plate and second plate. In certainimplementations, a first ion to neutral flux ratio from a first plasmazone, through the plate assembly and into the lower sub-chamber isdifferent from a second ion to neutral flux ratio from a second plasmazone, through the plate assembly and into the lower sub-chamber.

These and other features will be described below with reference to theassociated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a plasma etching reactor according to adisclosed embodiment.

FIGS. 2A-2B show close-up views of aligned (FIG. 2A) and misaligned(FIG. 2B) apertures in a plate assembly, depicting which species areable to pass through the assembly in each case.

FIG. 2C is a chart showing the Flux of Neutral Species vs. Position NearAperture for the line-of-sight (i.e., aligned) and non-line-of-sight(i.e., misaligned) cases.

FIG. 3A is a flowchart illustrating a method of performing an etchingoperation according to a disclosed embodiment.

FIG. 3B is a flowchart illustrating a semiconductor fabrication contextin which a disclosed etching operation may take place.

FIGS. 4A-4C show example series of injection control rings according tocertain disclosed embodiments.

FIG. 5 shows an example of a plasma etching apparatus having multipleseparate plasma zones according to a disclosed embodiment.

DETAILED DESCRIPTION

In this application, the terms “semiconductor wafer,” “wafer,”“substrate,” “wafer substrate,” and “partially fabricated integratedcircuit” are used interchangeably. One of ordinary skill in the artwould understand that the term “partially fabricated integrated circuit”can refer to a silicon wafer during any of many stages of integratedcircuit fabrication thereon. A wafer or substrate used in thesemiconductor device industry typically has a diameter of 200 mm, or 300mm, or 450 mm. Further, the terms “plate” and “grid” are usedinterchangeably. The following detailed description assumes theinvention is implemented on a wafer. However, the invention is not solimited. The work piece may be of various shapes, sizes, and materials.In addition to semiconductor wafers, other work pieces that may takeadvantage of this invention include various articles such as printedcircuit boards and the like.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented embodiments.The disclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Further, though the description often refers to “upper” and “lower”elements (or similarly to “top” and “bottom,” “left” and “right,” etc.)these descriptors are used in a non-limiting fashion, solely for thesake of clarity. One of ordinary skill in the art would understand thatother configurations may be used, as well. In certain embodiments,elements which are described herein as “upper” and “lower” may becomethe “lower” and “upper” or “left” and “right” elements, for example.

The embodiments herein generally deal with semiconductor processingmethods and apparatus. More specifically, the embodiments relate tomethods and apparatus for etching a semiconductor substrate. Inpracticing the disclosed techniques, a substrate is provided in aprocessing chamber. FIG. 1 shows a cross-sectional view of anappropriate processing apparatus 100. The reaction chamber is dividedinto an upper sub-chamber 132 and a lower sub-chamber 134 by a plateassembly 150. The plate assembly 150 includes an upper plate 116 and alower plate 130. Each of the upper and lower plates 116 and 130 haveapertures extending through the thickness of the plates. When theapertures in the upper and lower plates 116 and 130 are aligned, theypermit the passage of ions and neutral species from the uppersub-chamber to the lower sub-chamber. When the apertures in the upperand lower plates 116 and 130 are not aligned, neutral species are ableto pass through the misaligned apertures, while ions are substantiallyprevented from passing through.

This concept is shown in FIGS. 2A-2C. In FIG. 2A, the apertures in theupper plate 216 and lower plate 230 of the plate assembly 250 arealigned, and both ions (shown by the solid arrow) and neutral species(shown by the dotted arrow) are able to pass through into the lowersub-chamber. In FIG. 2B, the upper and lower plates 216 and 230 of plateassembly 250 are misaligned, and only the neutral species are able topass through. FIG. 2C shows the flux of neutral species at an exit ofthe lower plate when the apertures in the upper and lower plates arealigned (line-of-sight case, shown by the dotted line) and when theapertures are mis-aligned (non-line-of-sight case, shown by the solidline). Although the total flux of neutrals is lower in thenon-line-of-sight case, the decrease is only about 16%. This differencein neutral flux between the line-of-sight and non-line-of-sight cases isquite small when compared to the difference in ion flux between thesetwo cases.

Returning to the embodiment of FIG. 1, additional details of theprocessing apparatus 100 will be provided. The upper sub-chamber 132 isconfigured to contain an inductively coupled plasma and the lowersub-chamber 134 is configured to contain a capacitively coupled plasma.Further, the volume of the lower sub-chamber 134 is adjustable, and thelower plate 130 is configured to operate as a gas delivery showerheadfor delivering process gases from gas feed 104 to the lower sub-chamber134. Process gases may be separately delivered to the upper sub-chamber132 through gas feed 106, which feeds upper showerhead plate 112. Insome cases, the upper showerhead plate 112 is made from a material suchas silicon, silicon nitride, silicon carbide or quartz. The uppershowerhead plate 112 may be slotted. Further, the upper showerhead plate112 may move toward and away from the substrate to decrease or increasethe amount of space between the upper and lower plates 116 and 130. Thismovement may help control the flux of radicals through the plateassembly 150 in certain embodiments.

Above the upper showerhead plate 112, there may be an insulator plate110 (e.g., a ceramic insulator plate). TCP coils 108 may be situatedabove the insulator plate 110. In the embodiment of FIG. 1, dual TCPcoils 108 are used. In embodiments where the upper zone plasma is not aninductively coupled plasma, these coils 108 may be absent. The reactorwalls 114 surround the lower and upper sub-chambers 134 and 132,respectively. In some embodiments, the reactor walls 114 are made fromanodized aluminum. The reactor walls 114 may also be coated with aprotective material such as, for example, Y₂O₃, or another materialdesigned to protect the semiconductor apparatus from harsh plasmaconditions. Further, in various embodiments, the reactor walls 114 mayinclude temperature control elements such as a temperature controlheater ring 128. These temperature control elements help to producedesirable plasma conditions within the upper and lower zone plasmas.

Upper plate 116, sometimes also referred to as an injection controlplate, is situated near the bottom of the upper sub-chamber 132. Thisupper plate 116 is rotatable about an axis normal to the face of theplate, and contains holes and/or slots which at least partially registerwith the slots/holes in the underlying lower plate 130. In theembodiment of FIG. 1, the upper plate 116 is insulating and the lowerplate 130 is conductive and grounded. By rotating upper plate 116, theplate assembly open area changes, and different relative amounts ofspecies from the upper zone plasma are able to travel through the plateassembly 150 and into the lower sub-chamber 132. The plate assembly openarea (sometimes referred to more simply as assembly open area) isdefined as the area of the plate assembly through which there is a clearline-of-sight from the upper sub-chamber 132 to the lower sub-chamber134 at a given time. In other words, it represents the amount of area inwhich the apertures in the upper and lower plates 116 and 130 arealigned. The plate assembly open area may change based on the degree ofalignment of the apertures in the plate assembly. The maximum plateassembly open area is defined as the highest assembly open areaattainable for a given set of plates. Similarly, the term plate openarea is defined as the area of a single plate through which there is aclear line-of-sight from the upper- to lower sub-chambers 132 and 134.In various embodiments, rotating upper plate 116 allows for tuning ofthe relative amounts of charged and neutral species passing from theupper to lower sub-chambers, as described elsewhere herein.

Other features highlighted in FIG. 1 include a pressure control ring 118(often made from an insulating material such as quartz), a high powertunable electrostatic chuck 120, a coaxial RF switch 122, a coolingspacer ring 126 (often used to house fluid, including but not limited towater), and a temperature control heater ring 128. Further, distance 124indicates that the height of the lower sub-chamber may be adjustable.

Methods

FIG. 3A provides a flow chart for etching a material in accordance withvarious embodiments herein. Process 300A begins at block 301, where asubstrate having material for removal is received in the lowersub-chamber of a processing apparatus. An exemplary processing apparatusis described above in relation to FIG. 1. At block 303, plasma isgenerated in the upper sub-chamber of the processing apparatus. At block305, a bias is applied to the substrate support. In some cases, thisbias causes a plasma to form in the lower sub-chamber. In other cases,the bias may be sufficiently weak (e.g., in terms of frequency and/orapplied power) such that there is substantially no plasma present in thelower sub-chamber. In either case, the bias acts to attract ions towardthe substrate for processing. At block 307, the relative flux of ionsand neutral species from the upper sub-chamber, through the ionextractor plate, and into the lower sub-chamber is controlled. The fluxof ions is primarily controlled by changing the amount of plate assemblyopen area. Increasing the amount of plate assembly open area directlyand substantially increases the ion flux through the plate assembly.Although increasing the plate assembly open area also increases the fluxof neutral species, as shown in FIG. 2C, the flux of neutral species issignificantly less affected by this open area, as compared to the fluxof ions.

The flux of neutral species is primarily affected by the distancebetween the upper and lower plates. Increasing the distance between thetwo plates increases the amount of neutral species that are able to passthrough. Wider gaps between the plates create more open, less tortuouspaths through which the neutral species may travel to reach an aperturein the lower plate. In some implementations, the plate assembly openarea and/or the distance between the upper and lower plate may changeduring processing of a substrate. Of course these variables may alsochange between processing different substrates, as may be needed fordifferent types of applications. The process 300A continues at block309, where the substrate is etched. In some cases, reactive etchingchemistry may be provided to the upper and/or lower sub-chambers to helpachieve the etching. In other cases, the etching is realized through ionetching without the help of reactive chemistry.

FIG. 3B illustrates an exemplary semiconductor fabrication process thatmay benefit from the disclosed techniques. In particular, FIG. 3Brelates to a broader fabrication context in which the etching processdescribed in FIG. 3A may take place. An example of this broadersemiconductor fabrication method is further discussed and described inU.S. Pat. Nos. 6,689,283, titled DRY ETCHING METHOD, MICROFABRICATIONPROCESS AND DRY ETCHING MASK; and RE40,951, titled DRY ETCHING METHODFOR MAGNETIC MATERIAL, each of which is incorporated herein by referencein its entirety.

The process 300B begins at block 302, where a stack of materials isdeposited on a substrate. In one embodiment, the stack is made ofalternating layers of conductive and insulating materials. In variouscases, the substrate on which the stack is deposited is a semiconductorwafer. Next, at block 304, a resist layer is deposited on the stack ofalternating layers. The resist layer may be micro-patterned using alithography technique. In a particular case, the patterned resist layeris e.g., a positive-type resist deposited using a spin-coating methodand patterned using UV or electron-beam exposure equipment. At block306, a mask layer is deposited on the patterned resist layer. In somecases, the mask layer is made of titanium nitride (TiN), which may bedeposited through a reactive sputtering method.

Next, at block 308, the patterned resist layer is removed to form apatterned mask layer. In some embodiments, the removal may beaccomplished through a lift-off method by dipping the substrate in asolvent bath and applying ultrasonic energy to remove the patternedresist. Next, the stack on the substrate may be etched at block 310 toform an etched stack. The etching may occur through the disclosed plasmaetching techniques. For example, the process 300A shown in FIG. 3A maybe implemented in operation 310.

Etching Mechanism

The techniques described herein may be beneficial in implementing avariety of etching processes that may occur through an assortment ofmechanisms. In some cases, the removal of unwanted material may beaccomplished through the use of ion etching (i.e., ion sputtering or ionmilling) alone. In other embodiments, reactive chemistry is used alongwith ion exposure to facilitate material removal in a process referredto as reactive ion etching.

Ion etching generally refers to the removal of atoms by physicalsputtering with an inert gas. Physical sputtering is driven by momentumexchange between the ions and the materials with which they collide.Upon impact, the incident ions set off collision cascades in the target.When such cascades recoil and reach the target surface with an energygreater than the surface binding energy, an atom may be ejected, knownas sputtering.

Reactive ion etching generally refers to the removal of material throughthe action of chemically active ions and/or radicals, which may reactwith the unwanted material to aid in its removal. Where reactivechemistry is used, one purpose of the ions may be to activate thesurface for reaction. Without wishing to be bound by any theory ormechanism of action, it is believed that ion bombardment may generateactive sites on the substrate by creating dangling bonds and/or otherphysicochemically receptive features on the metal or other material tobe etched. In some cases, a combination of ion sputtering and radicalinduced reactions are used.

During processing, gas may be delivered solely to the upper sub-chamber,solely to the lower sub-chamber, or to both sub-chambers. The gasesdelivered to each sub-chamber may be the same or different (e.g.,different gases, or different concentrations of the same gases). The gasused to create the plasmas may be chosen to reduce or eliminate unwantedreactions in the reaction chamber, based in part on the etchingchemistry used and the material to be etched. The materials listedherein are merely exemplary and are not meant to limit the embodimentsin any way. One of ordinary skill in the art would understand that thetechniques herein may be used with a variety of materials and reactions.

In some cases, the gas delivered to the upper and/or lower sub-chambercontains an inert gas such as Ar, He, Ne, Kr, etc. Where etching isachieved through ion sputtering, inert gases may be the only gasessupplied to the sub-chambers. However, where etching occurs throughreactive ion etching, the gas delivered to the upper and/or lowersub-chamber may include a reactive gas (e.g., an etchant and/or anadditional reactive processing gas). Examples of reactive gases that maybe used include flourocarbons (C_(x)F_(y)), hydrocarbons (C_(x)H_(y)),hydrogen (H₂), oxygen (O₂), nitrogen (N₂), methane (CH₄), carbontetrafluoride (CF₄), chlorine (Cl₂), hydrogen bromide (HBr), ammonia(NH₃), phosphorus trifluoride (PF₃), carbonyl fluoride (COF₂), carbonmonoxide (CO), nitric oxide (NO), methanol (CH₃OH), ethanol (C₂H₅OH),acetylacetone (C₅H₈O₂), hexafluoroacetylacetone (C₅H₂F₆O₂), thionylchloride (SOCl₂), thionyl fluoride (SOF₂), acetic acid (CH₃COOH),pyridine (C₅H₅N), and/or formic acid (HCOOH). In various embodiments, acombination of these etching reactants is used. For example, in somecases a combination of CO+NO is used. In another case, a combination ofCO₂+NO₂ is used. In a further case, pyridine is combined with thionylchloride and/or thionyl fluoride. In certain cases, reactive gases areonly supplied to the upper or lower sub-chamber, while in other casesreactive gases may be supplied to both sub-chambers. Furthermore, insome embodiments, an additional process gas is delivered (e.g., to thelower sub-chamber) in order to perform a specific function. For example,the additional process gas may be provided to protect a surface (e.g.,to protect a mask layer). The additional process gas may be providedbefore or during an etch process. In some implementations, a combinationof inert and reactive gases are used.

Any type of gas inlets may be used, for example gas showerheads, centralinlet nozzles, or a plurality of inlet nozzles located at differentpoints in the sub-chambers (e.g., around the periphery of asub-chamber). In one embodiment, the lower plate of the plate assemblyis used as a gas distribution showerhead. In this case, the lower plateincludes channels for delivering process gases to the lower sub-chamber.

A few particular possibilities for gas delivery will be specified,though these examples are not intended to limit the embodiments. In oneimplementation, one or more etchant species are delivered to the lowersub-chamber through the lower plate of the plate assembly, which acts asa showerhead. In another implementation, etchant is delivered to thelower sub-chamber through a port or ports that are not part of ashowerhead. In a further implementation, both etchant and additionalreactive processing gas are delivered to the upper sub-chamber. In yetanother implementation, both etchant and additional reactive processinggas are delivered to the lower sub-chamber. In an additionalimplementation, described more fully below, distinct mixtures of gasesmay be supplied to different radial portions (e.g., concentricring-shaped portions) of the upper sub-chamber.

In some implementations, the material to be etched is Si, SO₂, SiN,SiON, SiCOH, TiN, W, Al, a low-K material, a high-k material, etc. Incertain embodiments, the substrate to be etched is a partiallyfabricated MRAM or ReRAM device. Further, the material to be etched maybe a stack of materials deposited on a substrate. The stack may havealternating/interleaving layers of dielectric and conductive materials.

In some embodiments, additional process gases are used in combinationwith inert gas and reactive etch chemistry. These additional processgases may be “tuning gases” used to adjust the plasma conditions presentin a plasma region. One condition that may be tuned through addition ofa tuning gas is the degree of fragmentation of etching species. Forexample, in certain embodiments, oxygen, hydrogen and/or argon may beused to recombine certain fragmented etchant species. Other examples oftuning gases that may be used include the reactive gases listed above.The additional process gases may include gases used to passivate asurface (or a portion thereof) such that the surface is protected frometching. Examples of passivating gases include H₂, Cl₂, CxFy, CxHy etc.

Position of the Plate Assembly in the Reactor

The plate assembly is positioned in the reaction chamber, therebydividing the reaction chamber into upper and lower sub-chambers. Anexample of a chamber suitable for modification to include a plateassembly as described herein is a Kiyo Reactor from Lam ResearchCorporation of Fremont, Calif. For context, the following descriptionmay be considered with reference to FIG. 1, which is further describedabove. In certain implementations, the plate assembly 150 is positionedsuch that the distance between the lower surface of the lower plate andthe upper surface of the substrate is between about 10-50 mm. The heightof the upper sub-chamber may be chosen based on, for example, poweroptimization considerations. Larger upper sub-chambers will requiregreater power usage in order to sustain a plasma in the larger region.In some embodiments, the height of the upper sub-chamber is betweenabout 2-20 inches, for example between about 5-15 inches. In aparticular embodiment, the upper sub-chamber has a height of about 11inches.

The plate assembly should not be positioned too close to the wafer, asthis may cause printing of the plate pattern to occur on the wafer'sface. In other words, the pattern of slots/holes in the plate mayundesirably appear on the face of the wafer after processing, causingsevere etch non-uniformity on the substrate surface. For manyapplications, a separation distance of at least about 10 mm issufficient.

Design of the Plate Assembly

A basic embodiment of the plate assembly is provided in this section.Additional details relating to alternative designs of the plate assemblycan be found in the Promoting Radially Uniform Results section below.

The plate assembly includes two plates/grids having aperturestherethrough. The plates are positioned on top of one another such thatthere is an upper plate and a lower plate separated by a small distance(e.g., between about 1-6 mm). The upper and lower plates aresubstantially parallel to one another (e.g., within about 10°). In someembodiments, the plates are between about 3-20 mm thick, for examplebetween about 5-15 mm thick, or between about 6-10 mm thick. If a plateis too thick, or if the perforations in the plate are too small, theplate may block too many ions from passing through (i.e., ions willcollide with the plate, sometimes on a sidewall of an aperture in theplate, instead of passing through it). If a grid is too thin, it may notbe adequately rigid, it may not be able to withstand plasma processing,and it may need to be replaced fairly often. The grids should besufficiently rigid such that they do not bow or otherwise bend whenplaced in the reaction chamber. This helps to ensure uniform etchresults.

The plates may be made of a variety of materials including bothinsulating and conducting materials. Further, one or more of the platesmay be coated. In embodiments where a bias is applied to a plate duringetching, the material used to construct or coat the plate should beconductive. In various embodiments, one or more plates are constructedfrom or coated with metal or a metallic alloy. In these or otherembodiments, one or more of the plates is constructed from an insulatingmaterial. In some cases, one or more plates may be coated with a hardcarbon material. In some particular cases, the plates may be coated witha layer of Y₂O₃, YF₃, YAG, titanium nitride, or CeO₂. The grid materialmay or may not be anodized or otherwise passivated for, e.g., corrosionresistance. In one embodiment, the upper plate is made of an insulatingmaterial (e.g., quartz) and the lower plate is made of a conductivematerial (e.g., metal). Other configurations are possible within thescope of the disclosed embodiments.

The plate assembly generally spans a horizontal section of the chamber.Where the chamber is circular (as viewed from above or facing the workpiece), the plate assembly will also be circular. This allows theassembly to effectively divide the reaction chamber into twosub-chambers. In certain designs, the shape of the plate assembly isdefined by the geometry of the substrate (which is typically but notnecessarily a circular wafer). As is well known, wafers are oftenprovided in various sizes, such as 200 mm, 300 mm, 450 mm, etc. Othershapes are possible for square or other polygonal substrates orsmaller/larger substrates. Thus, the cross-section of the plate assembly(as viewed from above) may have a variety of shapes and sizes. In someembodiments, there may be a distance of separation between the plateassembly and the chamber walls. This distance may help prevent arcingbetween the plate assembly and the chamber walls. In certainembodiments, this distance is about 3 cm or greater.

By changing the orientation of one plate relative to the other plate,the ratio of ion flux to radical flux (referred to as the flux ratio,defined as the ion flux/neutral flux) may be controlled. One way thiscontrol occurs is by rotating a plate such that the apertures in theupper and lower plates are aligned. As described in relation to FIGS.2A-2B, aligned apertures permit the transfer of both ions and neutralspecies, while misaligned apertures largely only permit the transfer ofneutral species. Another way this control occurs is by changing thedistance between the two plates. A wider distance between the platesresults in a higher radical flux through the plate assembly, while anarrower distance results in a lower radical flux.

The apertures on the plates may take various shapes. For example, theapertures could be circular holes, slots, C-shaped apertures, T-shapedapertures, etc. The apertures may be oriented such that an axisextending through the center of the aperture is normal to the face ofthe plate. In a particular embodiment, all of the apertures are orientedin this manner. In another embodiment, some of the apertures may beoriented at a non-perpendicular angle relative to the plate. Theapertures on the upper and lower plates may be the same shape or may bedifferent. The alignment of the apertures on the upper and lower platesmay be the same or may be different. The apertures are designed suchthat when the plates rotate relative to one another, the amount of plateassembly open area changes. In some cases, the perforations may bedesigned such that little or no current is induced in a plate duringplasma generation. One design which ensures this result is a platehaving radially directed slots. Where the apparatus is not designed toprevent this type of problem, a current may be induced to flowsubstantially circularly around the plate or to flow in small eddycurrents on the grid, resulting in increased parasitic powerconsumption.

The aspect ratio of the apertures is defined as the width/diameter of anaperture divided by the depth of the aperture. Because the aperturesextend through the thickness of each plate, the depth of the aperture isequal to the plate thickness. The aspect ratio of the slots should besufficiently small such that plasma does not ignite within theapertures. The appropriate aspect ratio will depend on the plasmaconditions present in the upper sub-chamber. For example, where theupper sub-chamber contains a high pressure/high density plasma, theaspect ratio should be somewhat smaller. Similarly, where the uppersub-chamber contains a low pressure/low density plasma, the aspect ratiomay be somewhat larger (though there is flexibility in this case). Wherea high pressure/density plasma is used, the thickness of the plasmasheath is lower. As such, plasma is more likely to exist within theaperture, if the aperture is sufficiently wide. This phenomenon shouldbe avoided, for example by using an appropriately narrow aperture. Insome embodiments, the aspect ratio of the apertures is between about0.2-0.4. In these or other embodiments, the diameter or other principaldimension of an aperture may be between about 1-10 mm. The principaldimension is in a direction parallel to the work piece and spanning thelongest linear path in an aperture.

Both the plate open area and the plate assembly open area, definedabove, may be described in terms of absolute areas, or in terms of apercentage of the total area on the plate/assembly. For example, a 300mm diameter plate has an area of roughly 700 cm². If the plate has about350 cm² of open area, it may also be considered to have about 50% openarea. In some cases the plate open area and the maximum assembly openarea are equal. In other cases, the maximum plate assembly open area islower than the plate open area for one or more plates. In someimplementations, at least one plate has a plate open area between about30-70% or between about 40-60%. In these or other implementations, themaximum plate assembly open area may be between about 30-70% or betweenabout 40-60%.

As mentioned above, the plate assembly may also act as a showerhead fordelivering gas to one or more of the sub-chambers. In a particularembodiment, the lower plate of the plate assembly acts as a showerheadfor delivering gas to the lower sub-chamber. Similarly, the upper platecan be implemented as a showerhead for delivering gas to the uppersub-chamber. Where only a single plate of the assembly acts as ashowerhead, it may be the non-moving plate, as this configurationpresents fewer engineering considerations. A plate being used as ashowerhead will typically include one or more channels connecting gasfeed inlet(s) to a plurality of showerhead outlet holes.

In some implementations, the plate assembly has a region (e.g., acentral region) containing a feature for allowing a probing apparatus tobe disposed through the plate assembly. The probing apparatus can beprovided to probe process parameters associated with the plasmaprocessing system during operation. Probing processes can includeoptical emission endpoint detection, interferometeric endpointdetection, plasma density measurements, ion density measurements, andother metric probing operations. In certain embodiments, the centralregion of the plate assembly is open. In other embodiments, the centralregion of the assembly contains an optically clear material (e.g.,quartz, sapphire, etc.) to allow light to be transmitted through thegrid.

In some embodiments, the plate assembly may include cooling channelsembedded in one or more of the plates, and these cooling channels may befilled with a flowing or non-flowing coolant material. In certainembodiments, the cooling material is a fluid such as helium or otherinert gas or a liquid such as deionized (DI) water, process coolingwater, fluoroinert™ from 3M, or a refrigerant such as perfluorocarbons,hydrofluorocarbons, ammonia and CO₂. In these or other embodiments, theplate assembly may include embedded heating elements and/or atemperature measurement device. The cooling channels and embeddedheaters allow for precise temperature control, which permit closecontrol over the particle and wall conditions. This control may be usedto tune the conditions in the lower sub-chamber, in certain cases. Forexample, where the lower plate or plate assembly is maintained at acooler temperature, etch byproducts from the wafer may preferentiallydeposit on the lower plate, thereby reducing the gas phase density ofthe etch byproducts in the lower sub-chamber. Alternatively, the lowerplate or plate assembly may be maintained at an elevated temperature(e.g., above 80° C.) to reduce the deposition on the plate and ensurethat the chamber can remain relatively clean and/or reduce the timerequired to clean the chamber during waferless auto clean (WAC).

In some embodiments, the plates do not move (rotate or translate) whilean etch process is occurring. In such embodiments, the plates movebetween distinct steps, such as the individual steps of a multi-stepetch process used to fabricate complex structures such as MRAM stacks orFinFET gates. In other embodiments, the plates may rotate and/ortranslate during processing. This helps provide additional flexibilityfor processing, for example, where it is desired to have a differentratio of ion flux:neutral flux (i.e., flux ratio) at different times inan etching process. In one particular example, the ratio of ionflux:neutral flux through the plate assembly is higher toward thebeginning of an etch process and lower toward the end of an etchprocess. The opposite may be true in other implementations.

Additional details relating to alternative embodiments of the platassembly are included in the Promoting Radially Uniform Results sectionbelow.

Upper Sub-Chamber Conditions and Configuration

During processing, the upper sub-chamber typically contains a plasma.The plasma may be generated by various methods. In the embodiment ofFIG. 1, for example, the upper sub-chamber is configured to contain ahigh density (e.g., 10¹⁰ thru 10¹² charged particles/cm³) inductivelycoupled plasma. In other embodiments, the upper sub-chamber may beconfigured to contain a capacitively coupled plasma. Whatever plasmageneration technique is used, the plasma in the upper sub-chamber may bereferred to as a Radically Coupled Plasma (RCP). This term refers to aplasma that is spatially removed from the processing area directlysurrounding the substrate, from which radicals may be tunably extractedfor the purpose of processing a substrate. In this description, thephrase “tunably extracted” means that the relative flux of radicals andions (the flux ratio) may be tuned as desired for and/or during aparticular process.

Process gases that may be delivered to the upper sub-chamber aredescribed above in the Etching Mechanism section.

In certain embodiments, the power used to drive plasma formation inupper sub-chamber is between about 0-10,000 W, for example between about1,500-4,500 W. In a particular implementation the RF power used to driveplasma formation is about 3,000 W.

The pressure in the etching apparatus may be controlled by a vacuumpump. The vacuum pump may draw through exhaust ports on the reactionchamber. The exhaust ports may be located in the lower sub-chamberand/or in the upper sub-chamber. The exhaust ports may havevariable/controllable conductance. The orientation of the plate assembly(e.g., the alignment of the apertures and the distance between the upperand lower plates) may also affect the pressure experienced in thesub-chambers. Specifically, these orientation characteristics may betuned to provide an appropriate pressure gradient between the upper andlower sub-chambers.

In one mode of operation, the upper sub-chamber is not used, and allplasma generation and processing occur in the lower sub-chamber. Whenpracticing in this mode, the distance between the upper and lower platesof the plate assembly may be decreased to zero, and the apertures may bepurposely misaligned such that there is no plate assembly open area. Inthis mode, the etching apparatus basically simplifies down to a singlechamber conventional plasma etcher. All gases may be delivered directlyto the lower sub-chamber, where the substrate is situated. A plasma maybe generated in the lower sub-chamber, and the substrate may be etchedaccording to conventional methods. The ability to close off the uppersub-chamber and operate under conventional methods increases theflexibility and usefulness of the apparatus.

Lower Sub-Chamber Conditions and Bias Applied to Substrate Supporter

In various embodiments, a bias may be applied to the substrate supporterduring etching. Generally, where a substrate supporter (e.g., anelectrostatic chuck) is biased, the substrate is also biased. In somecases, the bias frequency is sufficiently large (e.g., about 60 MHz)such that a capacitively coupled plasma forms in the lower sub-chamber.In other cases, the bias frequency is much smaller (e.g., about 10 MHzor lower) such that there is substantially no plasma present in thelower sub-chamber during etching. In some embodiments, the power used tobias the substrate support is sufficiently low such that substantiallyno plasma is present in the lower sub-chamber, even where the frequencyof the bias is otherwise high enough to support plasma formation in thisregion. It may be beneficial to have a plasma present in the lowersub-chamber during etching in some embodiments. For example, where anetchant species is present in the lower sub-chamber and it is desired todissociate the etchant into more/smaller fragments, the existence of aplasma in the lower sub-chamber may help promote such dissociation.Other factors which may affect the degree of fragmentation of an etchantspecies include the density and effective electron temperature of plasmain the lower sub-chamber.

The gases supplied to the lower sub-chamber may include any of the gaseslisted above in the Etching Mechanism section.

The bias applied to the substrate support affects the energy level ofions striking the substrate. As such, the bias may be tuned to providean appropriate level of ion energy for a particular application. Otherfactors which affect the ion energy include the power supplied to theplasma sources in the upper sub-chamber, the electric field gradientacross the plate assembly (which may be controlled by the bias appliedto the lower plate of the assembly), and the pressure gradient betweenthe upper and lower sub-chambers.

Bias Applied to Plate Assembly

In some embodiments, a bias may be applied to one or more plates of theplate assembly. In one example, a negative bias is applied to the lowerplate of the plate assembly. In this way, ions produced in the uppersub-chamber and passing through the plate assembly may be acceleratedtowards the substrate at a particular ion energy. The bias on the platemay be tuned to provide a desired ion energy.

Promoting Radially Uniform Results

When etching a substrate, certain non-uniformities may arise. Inparticular, radial non-uniformity is a common issue when etchingsubstrates. In some instances, for example, etching may occur to agreater extent near a center area and edge area of a substrate whileoccurring to a lesser extent in a ring-shaped region between these twoareas. These radial non-uniformities are heightened when largersubstrates (e.g., 300 mm, and especially 450 mm substrates and larger)are being processed. It is desirable to reduce or eliminate thesenon-uniformities, where possible.

In some cases, the open area of the plate assembly is designed toprovide different levels of ion flux to different parts of thesubstrate. For example, where the open area is concentrated toward thecenter of the plate assembly, the ions may act on the center region ofthe wafer to a greater extent than on the edges of the wafer. Likewise,where the plate assembly open area is concentrated near the edge of theplate assembly, the ions may act on the edge regions of the wafer to agreater degree than the center of the wafer. These techniques may beespecially useful in combating center-to-edge non-uniformities. However,they may not afford sufficient flexibility in radial profiles of etchingconditions at the substrate surface.

Another technique for addressing the radial non-uniformity issue is byimplementing one or more of the plates of the plate assembly as a seriesof substantially concentric rings, instead of a single continuous plate.Where this is the case, the plate rings may be referred to as injectioncontrol rings, segments, or plate sections. Example collections ofinjection control rings/plate sections that may be used in place of anupper plate in the plate assembly are shown in FIGS. 4A-4C. Withreference to FIG. 4A, the series of rings 400A includes an outer ring402 and a middle ring 404 surrounding an inner plate 406. For the sakeof simplicity, inner plate 406 will be referred to as a ring despite thefact that it may not have a hole in the center. Each ring includes aplurality of apertures 408 through which ions and radicals may travel(under appropriate conditions). The series of rings 400B shown in FIG.4B includes four injection control rings (elements 412, 414, 416, and417 from the outside inwards), rather than the three rings shown in FIG.4A. In this embodiment, some injection control rings 412 and 414 includetwo concentric rows of apertures 408, while other injection controlrings 416 and 417 include three concentric rows of apertures. Manyvarieties of aperture placement may be used. For example, in the set ofinjection control rings 400C shown in FIG. 4C, each injection controlring includes a single row of apertures. As used in this section, the“rows” of apertures are circularly shaped (i.e., the rows do not referto linear rows). In the embodiment shown in FIG. 4C, each row ofapertures may be rotated independently of the other rows, since each rowis situated on its own dedicated injection control ring. While FIG. 4Cshows a set of rings 400C having 11 different plate sections, for thesake of clarity the individual plate sections/injection control ringsare not labeled.

In some embodiments, the density of apertures may vary between differentinjection control rings (e.g., a difference of at least 20%, or at least50%), while in other embodiments the density of apertures is uniform orsubstantially uniform (e.g., within about 20%) between differentinjection control rings.

By implementing one of the plates as concentric rings, it is possible toeasily radially tune the ratio of ion flux:radical flux. Each ring maybe rotated independently to provide a desired amount of open areathrough which ions and radicals may travel. For example, an outer ringmay be aligned such that ions can pass through the plate assembly to amaximum extent, while an inner ring may be aligned such that very few(or in some cases, even zero) ions can pass from the upper to lowersub-chamber.

Further, in some embodiments, each ring can independently movetoward/away from the other plate of the plate assembly in order to tunethe flux of radicals through each ring. Where this is the case, barriersshould be used to connect adjacent edges of the injection control rings.In the context of FIG. 4 where the rings are configured to translateindependently, a barrier should be included between the edge of innerplate 406 and the inner edge of middle ring 404. Similarly, a barriershould be included between the outer edge of middle ring 404 and theinner edge of outer ring 402. These barriers may be static, or they maymove with the injection control rings. The purpose of the barriers is toprevent the plasma in the upper sub-chamber from leaking into the lowersub-chamber. The minimum height of the barriers is dictated by thedifference in vertical position between adjacent injection controlrings.

Where injection control rings are used, each control ring may be biasedindependently to provide controlled ion energy and flux throughdifferent control rings. In one embodiment, the upper plate of the plateassembly is implemented as a single continuous plate, and the bottomplate of the assembly is implemented as a series of three injectioncontrol rings. A first bias is applied to the outer injection controlring, a second bias is applied to the middle control ring, and a thirdbias is applied to the inner injection control ring/plate. The first,second and third bias may be set to different levels to control ionenergy and flux as desired, particularly to promote radially uniformetch results. In some embodiments, defined segments or sectors of thebottom plate have independently controllable bias. In this way, ionenergy and flux can be controlled radially and/or azimuthally with adesired level of granularity. In some cases, the biasing mechanism is agrid of electrodes. In some cases, an electrode may be provided for eachhole in the bottom plate. The ratio of electrodes to bottom plate holesmay be 1:1, 1:2, 1:3, 1:4, 1:5, etc.

Because each ring can move independently of the others, it is easy toachieve different plating conditions over different parts of thesubstrate. This control may result in more uniform etching results overthe entire face of the substrate. This type of control is especiallybeneficial as the industry moves towards larger substrates (e.g., 450 mmdiameter or greater), where radial control of etching conditions is moreimportant. In some cases, the number of rings (including an inner centerplate) is between about 2-10, or between about 3-5. Greater numbers ofrings provide finer radial control over the etching conditions, but alsoentail greater engineering challenges. It has been observed that etchnon-uniformity commonly assumes a “W” shape with the center and edgeregions experiencing etch conditions that are more similar to oneanother than to the intermediate radial positions. In such settings, aplate assembly containing at least 3 rings may be effective foraddressing the inherent non-uniformity in the radial etch profile. Forexample, an intermediate ring may be rotated to produce a relativelyhigh ion:radical flux ratio in comparison to center and edge rings.

In some embodiments, the rings are the same width (for an annularlyshaped ring this width is measured as the distance between the inner andouter radii, for a circularly shaped “ring” this width is the radius) orsubstantially the same width (e.g., within about 10%). In otherembodiments, the rings may have different widths (e.g., the widths mayvary by at least about 10%, at least about 30% or at least about 50%).Where the rings have different widths, the wider rings may be positionedat or toward the periphery of the series of rings, at or toward thecenter of the rings, or at an intermediate position. This flexibilitypermits the optimization of an etching process depending on a particularapplication and its related non-uniformities.

Either the upper or lower plate (or both) may be implemented as a seriesof injection control rings. In a particular embodiment, the upper plateis made of a series of injection control rings made of an insulatingmaterial. In another particular embodiment, the lower plate is made of aseries of injection control rings made of a conductive material. Otherconfigurations are possible, as well. Embodiments where the lower plateis stationary and the upper plate is made of a series of movableinjection control rings may be preferable in terms of controllingtemperatures, material behavior, particle formation, RF return issues,etc. However, either configuration may be used.

Where injection control rings are used, mechanisms (e.g., microactuators built into the other plate of the plate assembly) should beincluded for independently moving (e.g., rotating and translating) eachring. The rotation causing mechanism and the translation causingmechanism may be implemented independently, or may be implemented aspart of a single movement causing mechanism. In one embodiment, movementcausing mechanisms are included in the non-moving plate (e.g., the lowerplate), which cause the moving plate (e.g., the upper plate) to rotateand/or translate. The movement causing mechanism may include structuresthat extend outwards towards the peripheral walls of the reactor, andmay extend through the non-moving plate. Where the apparatus includesinsulating walls dividing the upper sub- chamber into distinct plasmazones (discussed below in this section), the movement causing elementsmay extend through these insulating walls.

Only a small degree of movement is typically required. For example, arotation of between about 1-10°, or between about 1-5°, may besufficient. In various implementations, the amount of angular rotationis set to permit maximum ion:radical flux ratio and minimum ion:radicalflux ratio, and many or all ratios in between. For relatively smallapertures, the required amount of rotation may be quite small.Similarly, only a relatively small amount of translation is used in mostimplementations. For example, in some embodiments, the apparatus iscapable of independently translating each ring at least about 0.5 mm, orat least about 1 mm. In some cases, the rings may translate betweenabout 0-10 mm. In some implementations, etching will be conducted suchthat the distance between the plate and ring of an assembly in oneradial section is at least about 0.5 mm greater than the distancebetween the plate and ring of the assembly in a second radial section(the radial sections being coextensive with the injection controlrings).

A further technique for addressing the issue of radial non-uniformity isto implement the upper sub-chamber as a series of concentric plasmazones, rather than a single continuous upper plasma zone. An apparatusfor implementing this technique is illustrated in FIG. 5. The upperplasma zones may also be referred to more simply as plasma zones. Here,three plasma zones 132 a, 132 b and 132 c are employed. In otherembodiments, the number of plasma zones may range between about 2-10, orbetween about 3-5. In theory, any number of plasma zones may be used.Larger numbers of zones may be used to more finely tune the plasmaconditions, while smaller numbers of zones are simpler to implement. Assuggested above, many typical non-uniformity patterns can be addressedby having three radially separated sections with independent control ofion:radical flux ratios in the lower sub-chamber. In the embodimentdepicted in FIG. 5, the innermost plasma zone 132 a has a circularcross-section, as viewed from above. The other plasma zones 132 b-c haveannular cross-sections, as viewed from above, and surround the innermostplasma zone 132 a. The plasma zones 132 a-c are separated by insulatingwalls 142. In some cases, the insulating walls are made from adielectric material such as ceramic or quartz, though other insulatingmaterials may also be used. The purpose of the insulating walls 142 isto isolate each of the plasma zones 132 a-c from one another.

Each plasma zone has a separate gas feed inlet. For instance, plasmazone 132 a is fed by gas feed 106 a, while plasma zone 132 b is fed bygas feed 106 b, etc. The gas feeds are fed to a showerhead plate 141,which is capable of maintaining separation between the gas feeds anddelivering the correct feed to each plasma zone. Further, an independentpower source is provided for each plasma zone. In the embodiment of FIG.5, a multizone RF power supply 140 is used to independently providepower to the coils 108 proximate each plasma zone 132 a-c. By providingeach plasma zone 132 a-c with a separate gas feed 106 a-c and amechanism for providing power to each zone independently, differenttypes of plasma may be generated in each plasma zone 132 a-c. Thedifferent plasmas can help combat center-to-edge non-uniformities thatmay otherwise arise during etching.

In some embodiments, different compositions of gas are delivered to thedifferent plasma zones 132 a-c. For instance, a gas may be delivered tosome of the plasma zones while not being delivered to the other plasmazones. In one example, gas A may be delivered to plasma zones 132 a and132 c, and not to plasma zone 132 b. Similarly, in one embodiment adifferent tuning gas is delivered to each of the plasma zones 132 a-c.Another way to achieve different compositions of gas in the differentplasma zones is to deliver different relative concentrations ofcomponent gases to each plasma zone. In one example, plasma zones 132a-b receive a gas feed that is about 50% gas A and 50% gas B, whileplasma zone 132 c receives a gas feed that is about 75% gas A and about25% gas B. As used in this section, gases A and B can represent any ofthe appropriate gases mentioned in the Etching Mechanism section.

Other factors which may be variable or constant between the plasma zones132 a-c include the total flow rate delivered to each plasma zone, thepressure in each plasma zone, the temperature in each plasma zone, theplasma density in each plasma zone, the power delivered to the plasmasource for each zone, the frequency used to generate the plasma in eachzone, etc.

In a particular embodiment, separated plasma zones are implementedtogether with a series of injection control rings. The number of ringsand the number of plasma zones are typically equal, though this is notnecessarily always the case. The control rings may be designed such thatthey are the same width as (or are slightly smaller than) the plasmazones, such that a particular injection control ring effectively servesas the bottom surface of a corresponding plasma zone.

Example Modes of Operation

The methods and apparatus disclosed herein allow for a wide variety ofetching conditions to be achieved, both between processing differentsubstrates or different steps of a multi-step etching processes, andwithin processing a single substrate in a single process. As such, thedisclosed techniques may be used to implement many different kinds ofetching operations. A few types or modes of operation will be mentionedfor the sake of clarity and understanding. However, for the sake ofbrevity, certain types of processes that are enabled by the presentdisclosure will not be individually discussed. Further, the modes aredescribed in an exemplary fashion, and details related to the modes maybe altered according to a desired application. Certain variables(typically those that are not critical to operating the apparatus in aparticular mode of operation) may be excluded from the discussion in thefollowing sections.

Ion Bombardment Only

In this mode of operation, an inert gas is delivered to the uppersub-chamber and no etchant is used. Plasma is generated exclusively inthe upper sub-chamber and there is substantially no plasma present inthe lower sub-chamber. The energy of ions passing through the plateassembly into the lower sub-chamber may be tuned by controlling a biasapplied to the lower plate of the assembly. In various cases, theelectrostatic chuck is not biased when operating in this mode. The fluxof ions to the substrate can be controlled by any of the mechanismsdescribed herein (e.g., degree of alignment of apertures in plateassembly, injection control rings, distinct plasma zones, power suppliedto generate plasma, etc.).

Ion Bombardment in the Presence of Etchant

In this mode, a plasma generating gas is delivered to the uppersub-chamber and an etchant is delivered to either sub-chamber or both.The etchant may be fragmented or unfragmented. Where the etchant isdesired to be unfragmented, it should be delivered directly to the lowersub-chamber, and there should be substantially no plasma present in thisregion. The degree of fragmentation can be controlled by variousmechanisms, most notably the presence of plasma in the lowersub-chamber. Fragmentation can be tuned by controlling parameters suchas the electron temperature of the plasma and pressure in the lowersub-chamber.

In one example, an etchant may be fully dissociated or fragmented toproduce fluorine species and similar atomic or near atomic species.Examples of such an etchant include C_(x)F_(y) and C_(x)H_(y) gases.Alternatively, the etchant may be partially fragmented to multi-atometching components. In some cases the etchant species may beradicalized. The relative flux of ionic and neutral species (e.g.,radicalized fragmented etchant species) passing through the plateassembly into the lower sub-chamber may be controlled by any of themechanisms described herein (e.g., degree of alignment of apertures inplate assembly, injection control rings, distinct plasma zones, distancebetween upper and lower plate of the plate assembly, power supplied togenerate plasma, flow of ion-generating and radical-generating gasesinto upper sub-chamber, etc.).

Etchant Only

In this mode of operation, plasma is generated exclusively in the uppersub-chamber and the lower sub-chamber is substantially free of plasma.The plate assembly open area is set to zero (i.e., the apertures in theupper and lower plates are completely or substantially completelymisaligned). In this way, neutral species (e.g., radicalized etchantspecies) may pass through the plate assembly from the upper to lowersub-chamber, while ions are completely or substantially completelyprevented from entering the lower sub-chamber. The flux of neutralspecies may be controlled by, for example, changing the distance betweenthe upper and lower plates of the plate assembly.

Deposition/Passivation

In this mode of operation, an additional process gas is delivered to thelower sub-chamber in order to form a protective layer on parts of thesubstrate. In one example, SiCl₄ is delivered to help protect a masklayer. Other gases that may be used as passivating gases include, butare not limited to, C_(x)F_(y), C_(x)H_(y), COS, H₂, HBr, etc. Inanother example, the additional process gas acts to protect thesidewalls of a trench or another feature. This additional process gasmay be delivered separately (i.e., while etching is not occurring, forexample immediately prior to an etching operation), or it may occurduring an etching process.

Plasma in the Lower Sub-Chamber

Plasma may be present in the lower sub-chamber in various modes ofoperating the etch reactor. In one mode of operation, the uppersub-chamber is not used. The upper and lower plates of the plateassembly are positioned such that they are in contact with one another(i.e., the distance between them is decreased to zero), and theapertures are completely misaligned. Plasma generating gas (which cancontain one or more of the gases mentioned in the Etching Mechanismsection above) is delivered directly to the lower sub-chamber, and aplasma is generated in this region. In this mode of operation, theetching apparatus basically simplifies into a conventional singlechamber etch reactor.

Where plasma is present in the lower sub-chamber, the plasma istypically generated by applying a high frequency bias to theelectrostatic chuck/substrate support. Alternatively, the plates may bedesigned to permit plasma to leak from the upper sub-chamber to thelower sub-chamber in certain implementations. In various embodimentswhere a plasma is present in the lower sub-chamber, an etchant speciesis present, though this is not necessarily always the case.

Apparatus

The methods described herein may be performed by any suitable plasmaetching apparatus having the described modifications (e.g., a plateassembly, injection control rings and/or separate plasma zones, etc.). Asuitable apparatus includes hardware for accomplishing the processoperations and a system controller having instructions for controllingprocess operations in accordance with the present invention. Forexample, in some embodiments, the hardware may include one or moreprocess stations included in a process tool.

System Controller

In some embodiments, a system controller (which may include one or morephysical or logical controllers) controls some or all of the operationsof a process tool. The system controller will typically include one ormore memory devices and one or more processors. The processor mayinclude a central processing unit (CPU) or computer, analog and/ordigital input/output connections, stepper motor controller boards, andother like components. Instructions for implementing appropriate controloperations are executed on the processor. These instructions may bestored on the memory devices associated with the controller or they maybe provided over a network. In certain embodiments, the systemcontroller executes system control software.

The system control software may include instructions for controlling thetiming, mixture of process gas components (e.g., the composition of theetchant gas, the composition of the gas used to generate the plasma, anyother process gases, etc.), chamber pressure, chamber temperature, wafertemperature, current and potential applied to the chuck/wafer and anyother electrodes, the bias applied to each of the grids of the gridassembly, the bias applied to the electrostatic chuck, wafer position,plate position, and other parameters of a particular process performedby the process tool. System control software may be configured in anysuitable way. For example, various process tool component subroutines orcontrol objects may be written to control operation of the process toolcomponents necessary to carry out various process tool processes. Systemcontrol software may be coded in any suitable computer readableprogramming language.

In some embodiments, system control software includes input/outputcontrol (IOC) sequence instructions for controlling the variousparameters described above. For example, each phase of an etchingprocess may include one or more instructions for execution by the systemcontroller. The instructions for setting process conditions for a plasmageneration process phase may be included in a corresponding plasmageneration recipe phase. In some embodiments, the etching recipe phasesmay be sequentially arranged, so that all instructions for an etchingprocess phase are executed concurrently with that process phase.

Other computer software and/or programs may be employed in someembodiments. Examples of programs or sections of programs for thispurpose include a substrate positioning program, an upper sub-chambergas delivery composition control program, a lower sub-chamber gasdelivery composition control program, a gas inlet timing controlprogram, a plate assembly bias control program, a plate assemblyposition control program, an electrostatic chuck bias control program, apressure control program, a heater control program, and apotential/current power supply control program. Any of thesoftware/programs mentioned herein may contain instructions formodifying the relevant parameters during etching. In one example, aplate assembly bias control program may contain instructions to modifythe bias to one or more plates of the plate assembly during etching. Asa consequence, the ion energy of the ions traveling into the lowersub-chamber may be modified during the etch process.

In some cases, the controllers control one or more of the followingfunctions: delivery of etchant or other processing gas to the lowersub-chamber, delivery of plasma generation gas to the upper sub-chamber,plasma generation conditions in the upper and/or lower sub-chamber, thebias applied to each plate of the plate assembly, rotation/translationof the plates in the plate assembly, etc. For example, the delivery ofgas to the sub-chambers may be achieved by directing certain valves toopen and close at particular times. This allows the controller tocontrol both the timing of gas delivery, as well as the composition ofthe delivered gases. The controller may control plasma generationconditions by, for example, directing a power supply to provide power toa plasma generator (e.g., the coils of an ICP reactor) at particularfrequencies/power levels. Further, the controller may control the plasmageneration conditions by directing a flow of inert gas (and/or in someembodiments reactive gas) to enter the upper sub-chamber, or bycontrolling the pressure in the sub-chambers, or by controlling thetemperature in the sub-chambers, etc. The controller may control therotation/translation of the plates in the plate assembly by directing arotational actuator and/or translational actuator to move the plates asdesired. In some cases, the controller is designed or configured torotate or translate a concentric plate section to control center to edgeetch conditions on the substrate. Similarly, the controller may bedesigned or configured to move at least one concentric plate sectionrelative to the first plate to orient the apertures of the first andsecond plates to control an ion to radical flux ratio. In oneembodiment, the controller is designed or configured to independentlycontrol plasma generation in the concentric plasma zones and therebycontrol center to edge etch conditions on the substrate. The controllersmay control these aspects based on sensor output (e.g., when current,current density, potential, pressure, etc. reach a certain threshold),the timing of an operation (e.g., opening valves at certain times in aprocess) or based on received instructions from a user.

The various hardware and method embodiments described above may be usedin conjunction with lithographic patterning tools or processes, forexample, for the fabrication or manufacture of semiconductor devices,displays, LEDs, photovoltaic panels and the like. Typically, though notnecessarily, such tools/processes will be used or conducted together ina common fabrication facility.

Lithographic patterning of a film typically comprises some or all of thefollowing steps, each step enabled with a number of possible tools: (1)application of photoresist on a workpiece, e.g., a substrate having asilicon nitride film formed thereon, using a spin-on or spray-on tool;(2) curing of photoresist using a hot plate or furnace or other suitablecuring tool; (3) exposing the photoresist to visible or UV or x-raylight with a tool such as a wafer stepper; (4) developing the resist soas to selectively remove resist and thereby pattern it using a tool suchas a wet bench or a spray developer; (5) transferring the resist patterninto an underlying film or workpiece by using a dry or plasma-assistedetching tool; and (6) removing the resist using a tool such as an RF ormicrowave plasma resist stripper. In some embodiments, an ashable hardmask layer (such as an amorphous carbon layer) and another suitable hardmask (such as an antireflective layer) may be deposited prior toapplying the photoresist.

It is to be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. As such, various acts illustrated may beperformed in the sequence illustrated, in other sequences, in parallel,or in some cases omitted. Likewise, the order of the above describedprocesses may be changed.

The subject matter of the present disclosure includes all novel andnonobvious combinations and sub-combinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

What is claimed is:
 1. A plate assembly for a reaction chambercomprising a plasma source, the plate assembly comprising: a firstplate; and a second plate comprising at least two substantiallyconcentric plate sections that are independently rotatable with respectto the first plate, wherein the first plate and second plate haveapertures extending through the thickness of each plate, and wherein thefirst plate and second plate are substantially parallel and verticallyaligned with one another such that either (i) the first plate is abovethe second plate, or (ii) the first plate is below the second plate. 2.The plate assembly of claim 1, wherein the second plate comprises atleast three substantially concentric plate sections.
 3. The plateassembly of claim 1, wherein at least some of the apertures in at leastone of the plates of the plate assembly have an aspect ratio betweenabout 0.2-0.4.
 4. The plate assembly of claim 1, wherein at least one ofthe plates of the plate assembly has an open area between about 40-60%.5. The plate assembly of claim 1, wherein the plate sections of thesecond plate comprise an insulating material and the first platecomprises a conductive material.
 6. The plate assembly of claim 1,coupled to a controller configured to rotate one or more of the platesections with respect to the first plate while a substrate is beingprocessed in the reaction chamber.
 7. The plate assembly of claim 1,wherein a distance between the first plate and the second plate isadjustable.
 8. The plate assembly of claim 7, coupled to a controllerconfigured to change the distance between the first plate and the secondplate while a substrate is being processed in the reaction chamber. 9.The plate assembly of claim 1, wherein at least one of the first plateand the second plate is configured to act as a showerhead for deliveringgases to the reaction chamber.
 10. The plate assembly of claim 1,wherein a distance between the first plate and the second plate isbetween about 1-6 mm.
 11. The plate assembly of claim 1, wherein thefirst plate is electrically conductive and the plate sections of thesecond plate are electrically insulating.
 12. The plate assembly ofclaim 1, wherein the first plate is electrically insulating and theplate sections of the second plate are electrically conductive.
 13. Theplate assembly of claim 1, further comprising micro-actuators configuredto move the plate sections of the second plate relative to the firstplate.
 14. The plate assembly of claim 13, wherein the micro-actuatorsare provided on the first plate.
 15. The plate assembly of claim 1,wherein the plate sections of the second plate are configured toindependently translate toward and away from the first plate.
 16. Acontroller for controlling an etching apparatus, the controller havinglogic to direct execution of a method of etching a substrate, the logiccomprising instructions to: (a) position the substrate in a reactionchamber of the etching apparatus comprising: (i) an upper sub-chamberand a lower sub-chamber, wherein the upper sub-chamber comprises atleast two substantially concentric plasma zones, wherein each plasmazone is isolated from other plasma zones by one or more insulatingwalls, (ii) a plate assembly positioned between the upper sub-chamberand lower sub-chamber and comprising a first plate and a second plate,wherein each plate has apertures extending through the thickness of theplate, and wherein the second plate is rotatable with respect to thefirst plate, (iii) one or more gas inlets to the upper sub-chamber, (iv)one or more gas outlets to the lower sub-chamber configured to removegas from the lower sub-chamber, and (v) a plasma generation sourceconfigured to produce a plasma in the upper sub-chamber, (b) flow plasmagenerating gas into and generate a plasma in each plasma zone, (c) flowneutral species present in the plasmas from the plasma zones, throughthe plate assembly, and into the lower sub-chamber, and (d) etch thesubstrate.
 17. The controller of claim 16, wherein the instructions for(b) comprise instructions to flow plasma generating gas of a firstcomposition into a first plasma zone and flow plasma generating gas of asecond composition into a second plasma zone.
 18. The controller ofclaim 16, wherein the instructions for (b) comprise instructions togenerate a first plasma in a first plasma zone and a second plasma in asecond plasma zone, wherein the first plasma and second plasma havedifferent densities.
 19. The controller of claim 16, wherein the logicfurther comprises instructions to control an ion to neutral flux ratiothrough the plate assembly by changing a distance between the firstplate and the second plate.
 20. The controller of claim 16, wherein afirst ion to neutral flux ratio from a first plasma zone, through theplate assembly and into the lower sub-chamber is different from a secondion to neutral flux ratio from a second plasma zone, through the plateassembly and into the lower sub-chamber.
 21. The controller of claim 16,wherein the second plate comprises at least two substantially concentricplate sections that are independently rotatable with respect to thefirst plate.